The present invention is directed to the fields of power conversion, signal processing, and related fields.
Many electronic AC to AC power converters and inverters employ a two-stage conversion process which converts an AC input power form to an intermediate DC voltage (the bus voltage) which is afterward converted into the desired AC output form. These converters may be called “multi-stage” because the input AC power form is converted in multiple stages—e.g., from AC to DC and then from DC back to AC—as opposed to a “single stage” converter that produces the output signal after a single conversion. Typical single stage converters are not as versatile as their multi-stage counterparts because the single stage topologies must usually sacrifice bidirectionality or symmetry of conversion for their single stage conversion simplicity.
AC to AC single stage converters illustrate these limitations. Due to the alternating polarity of AC signals, the polarity of the input voltage presented to these converters may be unpredictable, so converter designs need sophisticated means to adapt and compensate. For example, some converters may incorporate a diode-based rectifier circuit to ensure that the input voltage has an expected polarity or voltage. Such a rectifier significantly increases the expense and inefficiency of the system, particularly when the desired output voltage may not need to have the ability to reverse its polarity. Additionally, the rectifier makes it difficult, if not impossible, to achieve bidirectionality using the same circuit elements because of the presence of the diodes, so it is overly complicated to add additional inputs or outputs to the converter without introducing even more inefficiency and expense. Without the rectifier, alternative converters are typically multi-stage or not fully universal.